We did NCT (and Natal Hypnotherapy, but wouldn't really consider that an 'antenatal class' as such) and I highly recommend it. I didn't really learn anything new necessarily (but I work in the health field and had been reading and planning for this birth for literally years), but getting to meet other couples who were having a first baby at the same time was invaluable. My daughter is now nearly 4 months old and I see the girls from my NCT class at least every other week. They've been a wonderful source of support and become really close friends. The first 3 months or so of being a new parent are very overwhelming and isolating unless you have friends who are going through the same things you are. Having extra support is really important as all of my close friends either have older kids or aren't having kids yet, so there are no other new babies in our social circle.
I would have paid quite a bit for that added support, but you also don't have to. If you can't afford the full course fee, be in touch with your local NCT office about fee concessions. My husband and I are both professionals (self-employed, plus I'm a PhD student) so we aren't 'poor' but we aren't rich either and the full course fee would have been a struggle to pay at the time. The full fee for the course was about £260 but we only had to pay £60. I've heard some people say you can only get a reduced fee if you're on benefits, but we aren't and we make too much to qualify for any sort of benefit, but I just told them our total income and they gladly reduced the fee. It's worth asking.
If you're interested in using natural pain relief method (more so than learning about pregnancy/birth/parenting), I'd also highly recommend Natal Hypnotherapy. You can do it yourself at home with the CD (£12.50) and book (about £15?), but the one day course is only £95. The course is nice, but you really don't need it. I had a wonderful home birth and didn't need any pain relief using just NH.